A honeycomb structure made of a ceramics has been used as a catalyst carrier for an internal combustion engine, a boiler, a chemical reaction device, a reformer for a fuel cell and the like in which a catalyst function is used, a trapping filter (hereinafter referred to as a “diesel particulate filter (DPF)”) for fine particles in an exhaust gas, particularly diesel fine particles, and the like.
This type of ceramic honeycomb structure is constituted so that a plurality of porous honeycomb segments having a large number of through holes which are separated by partition walls and which extend through the structure in an axial direction are bound via adhesive layers (for example, see Patent Document 1). That is, the ceramic honeycomb structure is constituted so that a plurality of rows of the porous honeycomb segments having a square pole shape are combined and bonded to one another via the adhesive layers. At this time, the bonding is performed by interposing the adhesive layer between the bonding faces of the porous honeycomb segments and then imparting vibration to the honeycomb segments while applying a pressing force to the segments. That is, in a bonding step, first, a first porous honeycomb segment including an underlayer formed on the bonding face is disposed in the lowermost portion of the cut part of a support jig. Subsequently, a second porous honeycomb segment including an underlayer which is formed on one bonding face and which is coated with an adhesive is brought into close contact with the first honeycomb segment so that the bonding faces of the segments face each other via the adhesive. In this case, the end faces of the two honeycomb segments are pressed with a pressing plate and positioned in advance. Then, a pressing jig is allowed to abut on the subsequent honeycomb segment, thereby pressing the segment in a vertical direction, and the vibration is imparted in a direction in which the bonding faces are displaced from each other. In consequence, the first and second honeycomb segments can be bonded.
Subsequently, a third porous honeycomb segment including an underlayer which is formed on one bonding face and which is coated with an adhesive is brought into close contact with the first honeycomb segment so that the bonding face of the third porous honeycomb segment faces the other bonding face of the first honeycomb segment via the adhesive. In this state, the third honeycomb segment can be bonded to the first honeycomb segment in the same manner as in the second honeycomb segment. Furthermore, a fourth porous honeycomb segment including underlayers which are formed on two bonding faces and which are coated with an adhesive is arranged to come in close contact with the second honeycomb segment and the third honeycomb segment. In this state, the fourth honeycomb segment can be bonded to the second honeycomb segment and the third honeycomb segment in the same manner as in the second and third honeycomb segments.
However, in the conventional bonding method, the pressure and vibration are applied to each porous honeycomb segment, whereby the segments are successively bonded. Therefore, the vibration and pressurizing force are transmitted to the lower segment having an early stacking order until the last honeycomb segment is completely bonded. This transmitted force acts as a peeling force with respect to the honeycomb segments bonded to each other, which results in a problem that the adhesive layer bonded to the lower honeycomb segment peels and that a bonding strength partially decreases.
To solve such a problem, a method for bonding a ceramic honeycomb structure is suggested in which for a purpose of maintaining, as they are stacked, the adhesive layers bonded to the respective honeycomb segments regardless of the stacking order of the respective porous honeycomb segments and bonding all the honeycomb segments uniformly with a desired bonding strength, a plurality of porous honeycomb segments having a large number of through holes which are separated by the partition walls and which extend through the structure in the axial direction are bound via the adhesive layers to constitute the structure. The method for bonding the ceramic honeycomb structure is characterized in that the respective porous honeycomb segments are stacked with the adhesive layers interposed between the bonding faces of the respective segments. After the predetermined number of the porous honeycomb segments are stacked, the whole structure is simultaneously and finally pressurized via the porous honeycomb segment positioned in the outermost peripheral layer, and thereby the porous honeycomb segments are bonded (for example, see Patent Document 2).
However, in both the cases, a load is applied to flatten out a bonding material, so that the bonding material requires fluidity. Therefore, from a bonding time to a time when bonded portions develop strength (to a time when heat is applied in both the cases), there is a disadvantage such as the nonuniformity of a bonding width due to the contraction of the bonding material or the displacement of the bonded portions. The nonuniformity of the bonding width or the displacement of the bonded portions causes stress concentration during actual use, which generates a disadvantage such as cracking. The durability of the honeycomb structure might lower.
Patent Document 1: JP-A-2000-7455
Patent Document 2: JP-A-2004-262670